Basic and translational research has investigated the role of nm23 in the regulation of tumor metastasis. Reduced nm23 expression has been correlated with poor clinical course in many tumor cohorts, and transfection data indicate that re-expression of nm23 can reduce in vivo metastatic potential by 50-90%. Analysis of nm23-H1 allelic deletion, mutation and protein expression levels in a breast tumor cohort found that low protein expression was the most significant correlate of poor patient prognosis, indicating the importance of nm23-H1 transcriptional down-regulation. We have cloned the nm23-H1 promoter, and identified a 250 bp region which is responsible for its differential regulation between the nonmetastatic MCF-7 and metastatic MDA-MB-435 human breast carcinoma cell lines. The region contains a triad of transcription factor binding sites reported to mediate breast specific gene expression. The biochemical mechanism of Nm23 metastasis suppression is under investigation. We have identified a novel serine phosphorylation of Nm23, and prepared site directed mutants of nm23-H1 to test the role of ser 44 and ser120, as well as other interesting amino acids. In vitro and in vivo evaluation is underway. Experiments to identify proteins that Nm23 may specifically interact with are under investigation using transient transfections of epitope tagged nm23-H1 constructs. Using the COMPARE computer program in collaboration with DTP, DCT, NCI we have used Nm23 as a marker to identify 40 novel compounds with preferential in vitro inhibitory activity against the most aggressive human breast and melanoma cell lines. Two of these compounds are under further investigation for in vivo toxicity and efficacy, mechanism of action and effects of the metastatic process.